In a hybrid vehicle, an electric vehicle, or the like, a driving power is obtained since a motor is driven by electric power accumulated in a secondary battery such as a lithium ion battery or a nickel hydrogen battery.
In such a secondary battery, for example, a plurality of battery cells is mutually connected in series, thereby forming a battery pack.
With charge to and discharge from respective battery cells performed repeatedly, the battery pack gradually deteriorates over time and additionally, the output voltage of each battery cell changes.
Also, in the battery pack, the output voltage of each battery cell also changes due to a load variation, such as a change in the running state of a vehicle, or a disturbance such as a change in temperature or humidity.
In a case of the battery pack using lithium ion batteries, particularly, it is necessary to monitor the voltage and the like of each battery cell accurately to suppress overcharging to and overdischarging from each battery cell and therefore, techniques related to battery monitoring have been proposed (see PTL1 (JP 2013-024800 A)).
As illustrated in FIG. 3, a voltage detection device 520 of a conventional example described in PTL1 includes multiplexers 540, 541 that selectively connect any one of respective battery cells 511 of a battery pack 510 where the battery cell 511 is connected in series, and a plurality of voltage detection means 550, 551 for detecting the cell voltages as the output voltages of the multiplexers 540, 541.
Additionally, the voltage detection device 520 includes switching means 530 for switching the operation between a first mode where the respective voltage detection means 550, 551 detect the cell voltages of different battery cells 511 and a second mode where the respective voltage detection means 550, 551 detect the cell voltage of an identical battery cell 511.
With the voltage detection device 520 having such a configuration, by providing two measuring routes (the voltage detection means 550, 551, etc.) to measure an identical objective voltage respectively, if there is a difference between respective measurement results by the voltage detection means 550, 551, it is judged that any failure has arisen in either one or both of the measuring routes.